Option D: 'Oubliette' is 'a secret dungeon with access only through a trapdoor in its ceiling'.
This word means the same as the given group of words.
Hence it can replace the words and option D is correct.
Option A: 'Cellar' is 'a room below ground level in a house, used for storing wine or coal'.
Option B: 'Ditch' is 'a narrow channel dug at the side of a road or field, to hold or carry away water'.
Option C: 'Vault' is 'a large room or chamber used for storage, especially an underground one'.
These words do not mean the same as the given group of words and hence cannot replace them.
So, options A, B and C are wrong.